The present invention relates in general to a comparator, and more particularly to a high speed comparator circuit having the compatible open collector output in TTL(Transistor-Transistor Logic) using the single supply voltage.
In general monolithic linear IC(integrated circuit), The PNP transistor having the lateral structure becomes the limit element in constituting the high frequency circuit or the high speed comparator due to the inferior frequency characteristics the very low current amplification factor and the large variation of characteristic according to the operating current thereof.
The major conditions in the characteristics of a comparator are as follows: that firstly the non-symmetrical distortion of the output signal according to the amplitude variation of the input signal thereof must be small and the delay time must be constant, namely this means that the balance of rise and fall time and the minimization of delay skew must be accomplished; that secondly the switching speed must be fast; and that thirdly the variation of said first and second characteristics according to the variation of supply voltage must be small.
Meanwhile, the conventional comparator circuit as shown in FIG. 1 was constituted by coupling the NPN transistors Q25, Q26 and Q27 with the PNP transistors Q21, Q22, Q23 and Q24, but it has a defect in which it does not satisfy said three characteristics thereof. Also the high speed comparator of the type that is constituted by only NPN transistors without using PNP transistors is known, but it has many problems of complication thereof due to use of two power supply circuits, namely positive power supply and negative power supply.